The present invention relates to an improvement in a scroll compressor adapted to discharge fluid, such as a fluid refrigerant compressed in a pair of compression spaces, from a discharge port at the same time.
A conventional scroll compressor is constructed as shown in, for example, Japanese Patent Appln. Laid-open No. 175293/1986. A conventional example of a scroll compressor will now be described with reference to this publication. Referring to FIGS. 9 and 10, reference numeral 50 denotes a sealed container, in which a scroll compressor unit 51 and an electric motor unit 52 are housed. The scroll compressor unit 51 consists mainly of a fixed scroll member 53, an orbiting scroll member 54, an Oldham's ring 55, a driving shaft 56, a frame 57 and a metal bearing 58.
The fixed scroll member 53 is provided with a spiral wrap 60 extending from the lower surface of an end plate 59 at right angles thereto, which wrap 60 is formed so as to extend along an involute curve or a curve similar thereto and to have a constant thickness along substantially all its length. This scroll member 53 is further provided at its outer circumferential portion with a suction port 61 for a gas to be compressed, and a discharge port 62 at the central portion of the end plate 59. The fixed scroll member 53 is secured to the frame 57. The orbiting scroll member 54 is provided with an end plate 63, and a spiral wrap 64 extending from the upper surface of the end plate 63 at right angles thereto. The wraps 60, 64 of the fixed and orbiting scroll members 53, 54 are shaped in a mutually end-face symmetric relation and staggered from each other at 180.degree.. The fixed and orbiting scroll members 53, 54 are engaged with each other with the centers of the wraps thereof staggered by a distance equal to the radius of an orbiting movement of the orbiting scroll member 54. Accordingly, these two wraps 60, 64 contact each other at a plurality of points to form a plurality of compression spaces 65. The orbiting scroll member 54 is provided on its lower surface with a boss 66 into which the driving shaft 56 is inserted. The driving shaft 56 is supported on the frame 57 by the metal bearing 58. A rotor 67 in the electric motor unit 52 is mounted on one end portion of the rotary shaft 56, and the other end portion thereof is inserted into the boss 66 of the orbiting scroll member 54.
The winding starting angle of the wrap 60 of the fixed scroll member 53 is made to be larger than that of the wrap 64 of the orbiting scroll member 54. Namely, the length of the starting end portion of the wrap of the fixed scroll member 53 is made smaller than that of the corresponding portion of the orbiting scroll member 54.
In the scroll compressor of this construction, the length of the winding starting portion of the wrap 60 of the fixed scroll member 53 is set smaller, and a compression space 65A formed between the outer surface of the wrap of the fixed scroll member 53 and the inner surface of the wrap of the orbiting scroll member 54 and a compression space 65B formed between the inner surface of the wrap of the fixed scroll member 53 and the outer surface of the wrap of the orbiting scroll member 54 are made so as to be not communicated with a discharge port 62 simultaneously via a flow passage of a large cross-sectional area, whereby the occurrence of overcompression in one compression space 65A can be prevented.
Since the length of the winding starting portion of the wrap 60 of the fixed scroll member 53 is set smaller by increasing the winding starting angle of the same portion, the winding starting portion of the wrap 60 of the fixed scroll member 53 is separated from the wrap 64 of the orbiting scroll member 64 before the winding starting portion of the wrap 64 of the orbiting scroll member 54 has been separated from the wrap 60 of the fixed scroll member 53, so that the compression space 65A is communicated with the discharge port 62 before the compression space 65B. Consequently, a difference occurs between the pressure in the compression space 65A and that in the compression space 65B. Due to such a pressure imbalance in the compression spaces 65A, 65B, abnormal vibrations and abnormal sounds occur in the scroll compressor.